Power amplifier circuit, doherty amplifier circuit, multistage amplifier circuit, and power amplifier apparatus

ABSTRACT

A power amplifier circuit includes a first amplifier transistor, a first nonlinear element, and a current control circuit. The first amplifier transistor has a base or a gate into which a first signal is input, a collector or a drain from which a signal resulting from amplification of the first signal is output, and an emitter or a source that is grounded. The first nonlinear element is connected between the collector or the drain of the first amplifier transistor and the base or the gate of the first amplifier transistor. The current control circuit is connected between the ground and the base or the gate of the first amplifier transistor and controls current flowing through the first nonlinear element.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No.2021-119057 filed on Jul. 19, 2021. The content of this application isincorporated herein by reference in its entirety.

BACKGROUND ART

The present disclosure relates to a power amplifier circuit, a Dohertyamplifier circuit, a multistage amplifier circuit, and a power amplifierapparatus.

A transistor circuit capable of adjusting gain is provided (for example,refer to Japanese Unexamined Patent Application Publication No.52-130554).

In the transistor circuit described in Japanese Unexamined PatentApplication Publication No. 52-130554, an input signal input into aninput terminal is subjected to differential amplification in twotransistors and the input signal subjected to the differentialamplification is output from two output terminals. Since this transistorcircuit includes multiple differential amplifiers and multiple constantvoltage sources, the configuration of the circuit is complicated.

BRIEF SUMMARY

The present disclosure provides a power amplifier circuit, a Dohertyamplifier circuit, a multistage amplifier circuit, and a power amplifierapparatus, which are capable of realizing adjustment of gain inamplification of an input signal with simple circuit configurations.

A power amplifier circuit according to one aspect of the presentdisclosure includes a first amplifier transistor that has a base or agate into which a first signal is input, a collector or a drain fromwhich a signal resulting from amplification of the first signal isoutput, and an emitter or a source that is grounded; a first nonlinearcircuit element that is connected between the collector or the drain ofthe first amplifier transistor and the base or the gate of the firstamplifier transistor; and a current control circuit that is connectedbetween the ground and the base or gate of the first amplifiertransistor and that controls current flowing through the first nonlinearcircuit element.

According to the present disclosure, it is possible to provide a poweramplifier circuit, a Doherty amplifier circuit, a multistage amplifiercircuit, and a power amplifier apparatus, which are capable of realizingadjustment of gain in amplification of an input signal with simplecircuit configurations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a power amplifier circuit according to afirst embodiment of the present disclosure;

FIG. 2 is a circuit diagram of a power amplifier circuit according to asecond embodiment of the present disclosure;

FIG. 3 is a circuit diagram of a power amplifier circuit according to athird embodiment of the present disclosure;

FIG. 4 is a circuit diagram of a power amplifier circuit according to afourth embodiment of the present disclosure;

FIG. 5 is a circuit diagram of a power amplifier circuit according to afifth embodiment of the present disclosure;

FIG. 6 is a circuit diagram of a power amplifier circuit according to asixth embodiment of the present disclosure;

FIG. 7 is a circuit diagram of a power amplifier circuit according to aseventh embodiment of the present disclosure;

FIG. 8 is a circuit diagram of a power amplifier circuit according to aneighth embodiment of the present disclosure;

FIG. 9 is a circuit diagram of a multistage amplifier circuit accordingto a ninth embodiment of the present disclosure;

FIG. 10 is a circuit diagram of a variable gain amplifier in the ninthembodiment;

FIG. 11 is a circuit diagram of a gain control circuit in the ninthembodiment;

FIG. 12 is a circuit diagram of a Doherty amplifier circuit according toa tenth embodiment of the present disclosure; and

FIG. 13 is a circuit diagram of a gain control circuit in the tenthembodiment.

DETAILED DESCRIPTION

Embodiments of the present disclosure will herein be described in detailwith reference to the drawings. The same reference numerals and lettersare added to the same components and a duplicated description of suchcomponents is omitted herein.

First Embodiment

A power amplifier circuit according to a first embodiment will now bedescribed. FIG. 1 is a circuit diagram of a power amplifier circuit 101.As illustrated in FIG. 1 , a power amplifier apparatus includes compoundsemiconductor 1. The compound semiconductor 1 is manufactured in anintegrated circuit process using semiconductor containing, for example,compound of a group III element and a group V element as a principalcomponent. The semiconductor is, for example, semiconductor containinggallium arsenide (GaAs) as the principal component. The power amplifiercircuit 101 is formed in and on the compound semiconductor 1.

The power amplifier circuit 101 amplifies balanced signals including asignal RFp1 (a first signal) and a signal RFm1 (a second signal) andoutputs balanced signals including amplified signals RFp2 and RFm2. Thepower amplifier circuit 101 has variable gain. In other words, the poweramplifier circuit 101 is a variable gain differential amplifier circuit.

The power amplifier circuit 101 includes a current control circuit 11, afirst amplifier transistor 201, a second amplifier transistor 251,capacitors 202 and 252, resistive elements 203 and 253, inductors 204and 254, a diode 205 (a first nonlinear circuit element and a firstdiode), a diode 255 (a second nonlinear circuit element and a seconddiode), and a voltage power supply 207.

In the first embodiment, the transistors including the first amplifiertransistor 201 and the second amplifier transistor 251 are each composedof, for example, a bipolar transistor, such as a heterojunction bipolartransistor (HBT). The transistors including the first amplifiertransistor 201 and the second amplifier transistor 251 may each becomposed of another transistor, such as a metal oxidesemiconductor-field effect transistor (MOSFET). In this case, a base, acollector, and an emitter are replaced with a gate, a drain, and asource, respectively.

The signals RFp1 and RFm1 are input into input terminals 31 p and 31 m,respectively. In the first embodiment, the phase of the signal RFp1 isdifferent from the phase of the signal RFm1 by approximately 180°. Thephase difference may be greatly shifted from 180° depending on imbalanceof the wiring length in the circuit or the like.

The capacitor 202 has a first end connected to the input terminal 31 pand a second end. The resistive element 203 has a first end connected toa bias supply terminal 206 and a second end. Bias current or biasvoltage of the first amplifier transistor 201 is supplied to the biassupply terminal 206.

The first amplifier transistor 201 has a base connected to the secondend of the capacitor 202 and the second end of the resistive element203, a collector connected to an output terminal 32 p, and an emitterthat is grounded. The inductor 204 has a first end connected to thecollector of the first amplifier transistor 201 and a second endconnected to a positive electrode of the voltage power supply 207. Anegative electrode of the voltage power supply 207 is grounded.

The bias current or the bias voltage is supplied from the bias supplyterminal 206 to the base of the first amplifier transistor 201 throughthe resistive element 203. Voltage is applied from the voltage powersupply 207 to the collector of the first amplifier transistor 201through the inductor 204. The first amplifier transistor 201 amplifiesthe signal RFp1 input into the base and supplies the amplified signalRFp2 resulting from amplification of the signal RFp1 from the collectorto the output terminal 32 p.

The diode 205 has an anode connected to the collector of the firstamplifier transistor 201 and a cathode connected to the first end of thecapacitor 202. The diode 205 may be formed of a transistor having acollector connected to the collector of the first amplifier transistor201, a base connected to the collector of the diode 205, and an emitterconnected to the first end of the capacitor 202. Connection between thecollector of a transistor and the base of the transistor may behereinafter referred to as diode connection.

The capacitor 252 has a first end connected to the input terminal 31 mand a second end. The resistive element 253 has a first end connected toa bias supply terminal 256 and a second end. Bias current or biasvoltage of the second amplifier transistor 251 is supplied to the biassupply terminal 256.

The second amplifier transistor 251 has a base connected to the secondend of the capacitor 252 and the second end of the resistive element253, a collector connected to an output terminal 32 m, and an emitterthat is grounded. The inductor 254 has a first end connected to thecollector of the second amplifier transistor 251 and a second endconnected to the positive electrode of the voltage power supply 207.

The bias current or the bias voltage is supplied from the bias supplyterminal 256 to the base of the second amplifier transistor 251 throughthe resistive element 253. Voltage is applied from the voltage powersupply 207 to the collector of the second amplifier transistor 251through the inductor 254. The second amplifier transistor 251 amplifiesthe signal RFm1 input into the base and supplies the amplified signalRFm2 resulting from amplification of the signal RFm1 from the collectorto the output terminal 32 m.

The diode 255 has an anode connected to the collector of the secondamplifier transistor 251 and a cathode connected to the first end of thecapacitor 252. The diode 255 may be formed of a transistor that isdiode-connected.

The current control circuit 11 is connected between the ground, and thebase of the first amplifier transistor 201 and the base of the secondamplifier transistor 251 and controls current flowing through the diode205 and current flowing through the diode 255.

In the first embodiment, the current control circuit 11 includes atransistor 302 (a fourth transistor) and a transistor 303 (a fifthtransistor). The transistor 302 has a collector connected to the cathodeof the diode 205, the input terminal 31 p, and the first end of thecapacitor 202, a base connected to a variable gain amplifier (VGA)control signal input terminal 301, and an emitter that is grounded. Acontrol signal for controlling the current flowing through the diode 205and the current flowing through the diode 255 is supplied to the VGAcontrol signal input terminal 301.

The transistor 303 has a collector connected to the cathode of the diode255, the input terminal 31 m, and the first end of the capacitor 252, abase connected to the base of the transistor 302 and the VGA controlsignal input terminal 301, and an emitter that is grounded.

Parasitic capacitance 302 a exits between the collector of thetransistor 302 and the emitter thereof. Similarly, parasitic capacitance303 a exists between the collector of the transistor 303 and the emitterthereof. The parasitic capacitance 302 a and the parasitic capacitance303 a will be described in detail below.

(Amplification Operation of the Power Amplifier Circuit 101)

The first amplifier transistor 201 in the power amplifier circuit 101operates as a collector-output emitter-grounded circuit. Accordingly,the first amplifier transistor 201 supplies the amplified signal RFp2resulting from inverting amplification of the signal RFp1 to the outputterminal 32 p.

The provision of the diode 205 between the collector of the firstamplifier transistor 201 and the base thereof forms a return path fromthe collector of the first amplifier transistor 201 to the base thereof.Accordingly, the amplified signal RFp2 output from the collector of thefirst amplifier transistor 201 is returned to the base of the firstamplifier transistor 201 through the diode 205.

Since the voltage of the signal RFp1 has polarity reverse to that of thevoltage of the amplified signal RFp2, the amplified signal RFp2 returnedto the base of the first amplifier transistor 201 weakens the power ofthe signal RFp1. In other words, it is possible to reduce the gain ofthe first amplifier transistor 201 by feedback of the amplified signalRFp2 from the collector of the first amplifier transistor 201 to thebase thereof.

The diode 205 has a property in which its equivalent resistance value isvaried due to the current flowing through the diode 205. In the poweramplifier circuit 101, the collector current of the transistor 302 isadjusted using the control signal supplied to the base of the transistor302 through the VGA control signal input terminal 301. Increasing ordecreasing the collector current of the transistor 302 enables thecurrent flowing through the diode 205 to be increased or decreased.

In other words, since the adjustment of the current flowing through thediode 205 using the control signal enables the equivalent resistancevalue of the diode 205 to be adjusted, the amount of feedback of theamplified signal RFp2 from the collector of the first amplifiertransistor 201 to the base thereof is capable of being adjusted.Accordingly, it is possible to adjust the gain of the first amplifiertransistor 201.

As at the second amplifier transistor 251 side, since the adjustment ofthe current flowing through the diode 255 using the control signalenables the equivalent resistance value of the diode 255 to be adjusted,the amount of feedback of the amplified signal RFm2 from the collectorof the second amplifier transistor 251 to the base thereof is capable ofbeing adjusted. Accordingly, it is possible to adjust the gain of thesecond amplifier transistor 251.

Second Embodiment

A power amplifier circuit 102 according to a second embodiment will nowbe described. In the second embodiment and the subsequent embodiments, adescription of matters common to the first embodiment is omitted andonly points different from the first embodiment are described. Inparticular, the same effects and advantages of the same components arenot redundantly described in the respective embodiments.

FIG. 2 is a circuit diagram of the power amplifier circuit 102. Asillustrated in FIG. 2 , the power amplifier circuit 102 according to thesecond embodiment differs from the power amplifier circuit 101 accordingto the first embodiment in that the collector of a transistor 304 in acurrent control circuit 12 is connected to the first amplifiertransistor 201 and the second amplifier transistor 251 via inductors.

The power amplifier circuit 102 includes the current control circuit 12,instead of the current control circuit 11 in the power amplifier circuit101 illustrated in FIG. 1 . The current control circuit 12 includes thetransistor 304 (a third transistor) and a transformer 401. Thetransformer 401 includes a primary-side inductor 402 (a first line) anda secondary-side inductor 403. The secondary-side inductor 403 includesan inductor 403 a (a second line) and an inductor 403 b (a third line).

In the second embodiment, a signal RFp3 (a third signal) and a signalRFm3 (a fourth signal) are supplied to the input terminals 31 p and 31m, respectively. The phase of the signal RFp3 is shifted from the phaseof the signal RFm3 by approximately 180°. In other words, the signalRFp3 is balanced with the signal RFm3. The phase difference may begreatly shifted from 180° depending on imbalance of the wiring length inthe circuit or the like.

The primary-side inductor 402 has a first end connected to the inputterminal 31 p and a second end connected to the input terminal 31 m.

The inductor 403 a of the secondary-side inductor 403 iselectromagnetically coupled to the primary-side inductor 402 and has afirst end connected to the first end of the capacitor 202 and a secondend, which is a node 403 c.

The inductor 403 b is electromagnetically coupled to the primary-sideinductor 402 and has a first end connected to the second end of theinductor 403 a, which is the node 403 c, and a second end connected tothe first end of the capacitor 252. The inductor 403 b has approximatelythe same inductance as the inductance of the inductor 403 a.

The transistor 304 has a collector connected to the node 403 c, a baseconnected to the VGA control signal input terminal 301, and an emitterthat is grounded. Parasitic capacitance 304 a exists between thecollector of the transistor 304 and the emitter thereof.

(Amplification Operation and Effects and Advantages of the PowerAmplifier Circuit 102)

In the transformer 401, upon input of the signal RFp3 into the first endof the primary-side inductor 402 and input of the signal RFm3 into thesecond end thereof, the signal RFp1 is output from the first end of theinductor 403 a and the signal RFm1 is output from the second end of theinductor 403 b. The phase of the signal RFp1 is different from the phaseof the signal RFm1 by approximately 180°.

The signal RFp1 is amplified by the first amplifier transistor 201. Theamplified signal RFp2 resulting from the amplification of the signalRFp1 is output from the output terminal 32 p. The signal RFm1 isamplified by the second amplifier transistor 251. The amplified signalRFm2 resulting from amplification of the signal RFm1 is output from theoutput terminal 32 m.

In the power amplifier circuit 101 illustrated in FIG. 1 , the collectorof the transistor 302 and the collector of the transistor 303 aredirectly connected to the input terminals 31 p and 31 m, respectively.For example, when the signal RFp1 flows through the parasiticcapacitance 302 a of the transistor 302, reflected waves of the signalRFp1 may occur in the parasitic capacitance 302 a. Similarly, when thesignal RFm1 flows through the parasitic capacitance 303 a of thetransistor 303, reflected waves of the signal RFm1 may occur in theparasitic capacitance 303 a. When the signals RFp1 and RFm1 areradio-frequency signals (RF signals), the power of such reflected wavesis increased. The reflected waves are undesirable because the reflectedwaves reduce the quality of the signal or cause malfunction.

In addition, for example, when the signals RFp1 and RFm1 have largeamplitudes, the potential at the base of the transistor 302 may behigher than the potential at the collector thereof. At this time,current flows from the base of the transistor 302 to the collectorthereof to shift a bias point of the first amplifier transistor 201 ordecrease the current flowing through the diode 205. Also in thetransistor 303, current flows from the base of the transistor 303 to thecollector thereof to shift the bias point of the second amplifiertransistor 251 or decrease the current flowing through the diode 255.

In contrast, in the power amplifier circuit 102 illustrated in FIG. 2 ,since the collector of the transistor 304 is connected to the node 403 cof the secondary-side inductor 403 from which no radio-frequency signalis output, an occurrence of the reflected waves is prevented in theparasitic capacitance 304 a of the transistor 304. Accordingly, it ispossible to prevent a reduction in the quality of the radio-frequencysignal and an occurrence of malfunction.

In addition, it is possible to prevent the potential at the base of thetransistor 304 from being higher than the potential at the collectorthereof. This prevents the shift of the bias points of the firstamplifier transistor 201 and the second amplifier transistor 251 andstabilizes the current flowing through the diodes 205 and 255. In otherwords, it is possible to realize the variable gain differentialamplifier circuit that operates well for the radio-frequency signal.

Third Embodiment

A power amplifier circuit 103 according to a third embodiment will nowbe described. FIG. 3 is a circuit diagram of the power amplifier circuit103. As illustrated in FIG. 3 , the power amplifier circuit 103according to the third embodiment differs from the power amplifiercircuit 102 according to the second embodiment in that a resistiveelement is connected in series to each of the diodes 205 and 255.

The power amplifier circuit 103 further includes a resistive element 208(a first resistive element) and a resistive element 258, in addition tothe components in the power amplifier circuit 102 illustrated in FIG. 2. The resistive element 208 has a first end connected to the first endof the capacitor 202 and the first end of the inductor 403 a and asecond end connected to the cathode of the diode 205. The resistiveelement 208 may have a configuration in which the first end is connectedto the anode of the diode 205 and the second end is connected to thecollector of the first amplifier transistor 201.

The resistive element 258 has a first end connected to the first end ofthe capacitor 252 and the second end of the inductor 403 b and a secondend connected to the cathode of the diode 255. The resistive element 258may have a configuration in which the first end is connected to theanode of the diode 255 and the second end is connected to the collectorof the second amplifier transistor 251.

With the above configuration, the lower limit of combined resistancevalue of the resistive element 208 and the diode 205 is capable of beingadjusted using the resistance value of the resistive element 208.Accordingly, it is possible to adjust the lower limit of the gain of thefirst amplifier transistor 201.

Similarly, the lower limit of combined resistance value of the resistiveelement 258 and the diode 255 is capable of being adjusted using theresistance value of the resistive element 258. Accordingly, it ispossible to adjust the lower limit of the gain of the second amplifiertransistor 251.

The resistive element 208 may be connected in parallel to the diode 205.With this configuration, the upper limit of the combined resistancevalue of the resistive element 208 and the diode 205 is capable of beingadjusted using the resistance value of the resistive element 208.Accordingly, it is possible to adjust the upper limit of the gain of thefirst amplifier transistor 201.

Similarly, the resistive element 258 may be connected in parallel to thediode 255. With this configuration, the upper limit of the combinedresistance value of the resistive element 258 and the diode 255 iscapable of being adjusted using the resistance value of the resistiveelement 258. Accordingly, it is possible to adjust the upper limit ofthe gain of the second amplifier transistor 251.

Fourth Embodiment

A power amplifier circuit 104 according to a fourth embodiment will nowbe described. FIG. 4 is a circuit diagram of the power amplifier circuit104. As illustrated in FIG. 4 , the power amplifier circuit 104according to the fourth embodiment differs from the power amplifiercircuit 102 according to the second embodiment in that another diode isconnected in series to each of the diodes 205 and 255.

The power amplifier circuit 104 further includes a diode 209 (a seconddiode) and a diode 259, in addition to the components in the poweramplifier circuit 102 illustrated in FIG. 2 . The diode 209 has acathode connected to the first end of the capacitor 202 and the firstend of the inductor 403 a and an anode connected to the cathode of thediode 205.

The diode 259 has a cathode connected to the first end of the capacitor252 and the second end of the inductor 403 b and an anode connected tothe cathode of the diode 255. The diodes 209 and 259 may be formed oftransistors that are diode-connected.

With the above configuration, a variable range of the combinedresistance value of the diodes 205 and 209 is capable of being increasedto approximately two times of the variable range of the equivalentresistance value of the diode 205 in the power amplifier circuit 102.

Similarly, the variable range of the combined resistance value of thediodes 255 and 259 is capable of being increased to approximately twotimes of the variable range of the equivalent resistance value of thediode 255 in the power amplifier circuit 102. Accordingly, it ispossible to widen the adjustment ranges of the gain of the firstamplifier transistor 201 and the gain of the second amplifier transistor251, compared with those in the power amplifier circuit 102, and toincrease the maximum gain.

Fifth Embodiment

A power amplifier circuit 105 according to a fifth embodiment will nowbe described. FIG. 5 is a circuit diagram of the power amplifier circuit105. As illustrated in FIG. 5 , the power amplifier circuit 105according to the fifth embodiment differs from the power amplifiercircuit 102 according to the second embodiment in that voltagemultiplier circuits are provided, instead of the diodes 205 and 255.

The power amplifier circuit 105 includes voltage multiplier circuits 210and 260, instead of the diodes 205 and 255 in the power amplifiercircuit 102 illustrated in FIG. 2 .

The voltage multiplier circuit 210 includes a transistor 210 a (thefirst nonlinear circuit element and a first transistor), a resistiveelement 210 b (a second resistive element), and a resistive element 210c (a third resistive element). The voltage multiplier circuit 260includes a transistor 260 a (the second nonlinear circuit element and asecond transistor), a resistive element 260 b, and a resistive element260 c.

The transistor 210 a has a collector connected to the collector of thefirst amplifier transistor 201, a base, and an emitter connected to thefirst end of the capacitor 202. The resistive element 210 b has a firstend connected to the collector of the transistor 210 a and a second endconnected to the base of the transistor 210 a. The resistive element 210c has a first end connected to the base of the transistor 210 a and asecond end connected to the emitter of the transistor 210 a.

The transistor 260 a has a collector connected to the collector of thesecond amplifier transistor 251, a base, and an emitter connected to thefirst end of the capacitor 252. The resistive element 260 b has a firstend connected to the collector of the transistor 260 a and a second endconnected to the base of the transistor 260 a. The resistive element 260c has a first end connected to the base of the transistor 260 a and asecond end connected to the emitter of the transistor 260 a.

The operation of the voltage multiplier circuit will now be described.Since the voltage multiplier circuit 260 has a configuration similar tothat of the voltage multiplier circuit 210, the voltage multipliercircuit 210 is typically described here and a description of the voltagemultiplier circuit 260 is omitted herein.

For example, a state is considered in which collector current Ic of alevel causing a conduction state flows through the transistor 210 a.Since the transistor 210 a is in the conduction state, base-emittervoltage Vbe of the transistor 210 a is substantially constant (about 1.3V in the case of GaAs-HBT).

Since the voltage between the first end and the second end of theresistive element 210 c is equal to Vbe, current 12 flowing through theresistive element 210 c is calculated by dividing Vbe by a resistancevalue R2 of the resistive element 210 c, that is, Vbe/R2.

When the resistance value R2 is set to a low value so that base currentIb of the transistor 210 a is decreased to an extent that is ignorablewith respect to the current (R2<<Vbe/Ib), current I1 flowing through theresistive element 210 b is considered to be equal to the current I2(I1=I2).

Voltage V1 between the first end and the second end of the resistiveelement 210 b is calculated by multiplying a resistance value R1 of theresistive element 210 b by the current I1, that is, R1×I1. Since I1=I2and I2=Vbe/R2, V1=R1×Vbe/R2.

Accordingly, the voltage between the collector and the emitter of thetransistor 210 a is calculated by adding the voltage between both endsof the resistive element 210 b to the voltage between both ends of theresistive element 210 c, that is, (Vbe+R1×Vbe/R2)=Vbe×(1+R1/R2).

Since the base-emitter voltage Vbe of the transistor 210 a has asubstantially constant value, the voltage between both ends of thevoltage multiplier circuit 210 is substantially constant. Accordingly,adjusting the current flowing through the voltage multiplier circuit 210with the transistor 304 enables the equivalent resistance value betweenboth ends of the voltage multiplier circuit 210 to be adjusted. In otherwords, it is possible to adjust the gain of the first amplifiertransistor 201.

In addition, since appropriately selecting the resistance value of theresistive element 210 b and the resistance value of the resistiveelement 210 c enables the voltage between both ends of the voltagemultiplier circuit 210 to be arbitrarily set, the range of theequivalent resistance value between both ends of the voltage multipliercircuit 210 is capable of being adjusted. In other words, the range ofthe gain of the first amplifier transistor 201 is capable of beingadjusted. Consequently, it is possible to improve the degree of freedomof design of the power amplifier circuit 105.

Sixth Embodiment

A power amplifier circuit 106 according to a sixth embodiment will nowbe described. FIG. 6 is a circuit diagram of the power amplifier circuit106. As illustrated in FIG. 6 , the power amplifier circuit 106according to the sixth embodiment differs from the power amplifiercircuit 102 according to the second embodiment in that a single-endedsignal is input into the power amplifier circuit 106.

In the sixth embodiment, the transformer 401 functions as a balun. Asignal RF4 (the third signal), which is the single-ended signal, isinput into an input terminal 31. In the transformer 401, the first endof the primary-side inductor 402 is connected to the input terminal 31and the second end thereof is grounded. Upon input of the signal RF4into the first end of the primary-side inductor 402, the signal RFp1 isoutput from the first end of the inductor 403 a and the signal RFm1 isoutput from the second end of the inductor 403 b. The phase of thesignal RFp1 is shifted from the phase of the signal RFm1 byapproximately 180°.

With the above configuration, it is possible to realize the variablegain differential amplifier circuit that operates well for thesingle-ended signal in a high-frequency band.

Seventh Embodiment

A power amplifier circuit 107 according to a seventh embodiment will nowbe described. FIG. 7 is a circuit diagram of the power amplifier circuit107. As illustrated in FIG. 7 , the power amplifier circuit 107according to the seventh embodiment differs from the power amplifiercircuit 101 according to the first embodiment in that a current controlcircuit 13 is realized by one transistor.

The power amplifier circuit 107 includes the current control circuit 13,instead of the current control circuit 11 in the power amplifier circuit101 illustrated in FIG. 1 . The current control circuit 13 includes aninductor 305 (a first impedance element), an inductor 306 (a secondimpedance element), and a transistor 307 (a sixth transistor). Parasiticcapacitance 307 a exists between the collector and the emitter of thetransistor 307.

The inductor 305 has a first end connected to the cathode of the diode205, the input terminal 31 p, and the first end of the capacitor 202,and a second end. The inductor 306 has a first end connected to thecathode of the diode 255, the input terminal 31 m, and the first end ofthe capacitor 252, and a second end.

The transistor 307 has a collector connected to the second end of theinductor 305 and the second end of the inductor 306, a base connected tothe VGA control signal input terminal 301, and an emitter that isgrounded.

As described above, with the configuration including the inductors 305and 306 between the input terminals 31 p and 31 m, the current flowingthrough the diodes 205 and 255 is capable of being adjusted with onetransistor 307 to adjust the equivalent resistance values of the diodes205 and 255 while preventing short-circuiting of the input terminals 31p and 31 m with an alternating current signal. Consequently, it ispossible to adjust the gain of the first amplifier transistor 201 andthe gain of the second amplifier transistor 251 with one transistor 307.

Although the power amplifier circuit 107 is described to have theconfiguration including the inductors 305 and 306 as the impedanceelements, the configuration of the power amplifier circuit 107 is notlimited to this. The power amplifier circuit 107 may have aconfiguration including two resistive elements, instead of the inductors305 and 306.

Eighth Embodiment

A power amplifier circuit 108 according to an eighth embodiment will nowbe described. FIG. 8 is a circuit diagram of the power amplifier circuit108. As illustrated in FIG. 8 , the power amplifier circuit 108according to the eighth embodiment differs from the power amplifiercircuit 102 according to the second embodiment in that cross coupling isadopted in which a nonlinear circuit element is provided between thecollector of one amplifier transistor in a differential pair and thebase of the other amplifier transistor therein.

The power amplifier circuit 108 includes a transistor 211 (the firstnonlinear circuit element), a transistor 261(the second nonlinearcircuit element), and resistive elements 212 and 262, instead of thediodes 205 and 255 in the power amplifier circuit 102 illustrated inFIG. 2 .

The transistor 211 has a collector connected to the collector of thesecond amplifier transistor 251, a base connected to the first end ofthe capacitor 202, and an emitter connected to the collector of thetransistor 211.

The resistive element 212 has a first end connected to the base of thetransistor 211 and a second end connected to the collector of thetransistor 211.

The transistor 261 has a collector connected to the collector of thefirst amplifier transistor 201, a base connected to the first end of thecapacitor 252, and an emitter connected to the collector of thetransistor 261.

The resistive element 262 has a first end connected to the base of thetransistor 261 and a second end connected to the collector of thetransistor 261.

(Amplification Operation and Effects and Advantages of the PowerAmplifier Circuit 108)

Since junction capacitance 201 a is parasitized between the collectorand the base of the first amplifier transistor 201, a return path fromthe collector of the first amplifier transistor 201 to the base thereofis formed. The junction capacitance 201 a is decreased as the voltagebetween the collector and the base is increased and is increased as thevoltage between the collector and the base is decreased.

The amplified signal RFp2 output from the collector of the firstamplifier transistor 201 is returned to the base of the first amplifiertransistor 201 via the junction capacitance 201 a.

Reduction in the gain of the first amplifier transistor 201 anddegradation of input dependency of pass phase characteristicsundesirably occur due to the amplified signal RFp2 returned to the baseof the first amplifier transistor 201.

As in the second amplifier transistor 251, reduction in the gain of thesecond amplifier transistor 251 and degradation of the input dependencyof the pass phase characteristics occur due to junction capacitance 251a parasitized between the collector and the base of the second amplifiertransistor 251.

In order to resolve the above problems, the power amplifier circuit 108includes a path from the collector of the second amplifier transistor251 to the base of the first amplifier transistor 201 through a parallelcircuit of the transistor 211 and the resistive element 212 and thecapacitor 202. Junction capacitance 211 a is parasitized between thebase, and the collector and the emitter of the transistor 211.

Adjusting the control signal to be supplied to the base of thetransistor 304 enables the current flowing through the resistive element212 to be varied. This adjusts reverse bias to be applied to thetransistor 211 and adjusts the junction capacitance 211 a between thecollector and the base of the transistor 211.

The adjustment of the junction capacitance 211 a enables the amplitudeof the amplified signal RFm2 to be supplied from the collector of thesecond amplifier transistor 251 to the base of the first amplifiertransistor 201 through the junction capacitance 211 a and the capacitor202 to be varied. The amplified signal RFm2 to be supplied to the baseof the first amplifier transistor 201 through the junction capacitance211 a has a phase opposite to that of the amplified signal RFp2 to besupplied to the base of the first amplifier transistor 201 through thejunction capacitance 201 a. Accordingly, selecting the bias so that theamplified signal RFm2 has the same amplitude as that of the amplifiedsignal RFp2 offsets the amplified signal RFm2 and the amplified signalRFp2 to weaken the influence of the junction capacitance 201 a. In otherwords, weakening the influence of the junction capacitance 201 a, whichreduces the gain of the first amplifier transistor 201, causes most ofthe signal RFp1 from the inductor 403 a in the transformer 401 to besupplied to the base of the first amplifier transistor 201 to increasethe gain. Accordingly, it is possible to suppress the reduction in thegain of the first amplifier transistor 201 and the degradation of theinput dependency of the pass phase characteristics.

Since differentiating the amplitude of the amplified signal RFm2 to besupplied to the base of the first amplifier transistor 201 through thejunction capacitance 211 a from the amplitude of the amplified signalRFp2 to be supplied to the base of the first amplifier transistor 201through the junction capacitance 201 a decreases the signal RFp1, whichis supplied from the inductor 403 a to the base of the first amplifiertransistor 201, it is also possible to reduce the gain.

Similarly, the power amplifier circuit 108 includes a path from thecollector of the first amplifier transistor 201 to the base of thesecond amplifier transistor 251 through a parallel circuit of thetransistor 261 and the resistive element 262 and the capacitor 252.Junction capacitance 261 a is parasitized between the base, and thecollector and the emitter of the transistor 261.

Adjusting the control signal to be supplied to the base of thetransistor 304 enables the current flowing through the resistive element262 to be varied. This adjusts reverse bias to be applied to thetransistor 261 and adjusts the junction capacitance 261 a between thecollector and the base of the transistor 261.

The adjustment of the junction capacitance 261 a enables the amplitudeof the amplified signal RFp2 to be supplied from the collector of thefirst amplifier transistor 201 to the base of the second amplifiertransistor 251 through the junction capacitance 261 a and the capacitor252 to be varied. The amplified signal RFp2 to be supplied to the baseof the second amplifier transistor 251 through the junction capacitance261 a has a phase opposite to that of the amplified signal RFm2 to besupplied to the base of the second amplifier transistor 251 through thejunction capacitance 251 a. Accordingly, selecting the bias so that theamplified signal RFp2 has the same amplitude as that of the amplifiedsignal RFm2 offsets the amplified signal RFp2 and the amplified signalRFm2 to weaken the influence of the junction capacitance 251 a. In otherwords, weakening the influence of the junction capacitance 251 a, whichreduces the gain of the second amplifier transistor 251, causes most ofthe signal RFm1 from the inductor 403 b in the transformer 401 to besupplied to the base of the second amplifier transistor 251 to increasethe gain. Accordingly, it is possible to suppress the reduction in thegain of the second amplifier transistor 251 and the degradation of theinput dependency of the pass phase characteristics.

Since differentiating the amplitude of the amplified signal RFp2 to besupplied to the base of the second amplifier transistor 251 through thejunction capacitance 261 a from the amplitude of the amplified signalRFm2 to be supplied to the base of the second amplifier transistor 251through the junction capacitance 251 a decreases the signal RFm1, whichis supplied from the inductor 403 b to the base of the second amplifiertransistor 251, it is also possible to reduce the gain.

Although the power amplifier circuit 108 is described to have theconfiguration including the current control circuit 12, theconfiguration of the power amplifier circuit 108 is not limited to this.The power amplifier circuit 108 may have a configuration including thecurrent control circuit 11 or 13, instead of the current control circuit12.

Although the power amplifier circuit 108 is described to have theconfiguration including the transistors 211 and 261, the configurationof the power amplifier circuit 108 is not limited to this. The poweramplifier circuit 108 may have a configuration including diodes, insteadof the transistors 211 and 261.

Ninth Embodiment

A multistage amplifier circuit 109 according to a ninth embodiment willnow be described. FIG. 9 is a circuit diagram of the multistageamplifier circuit 109. As illustrated in FIG. 9 , the multistageamplifier circuit 109 according to the ninth embodiment differs from thepower amplifier circuit 102 according to the second embodiment in that avariable gain amplifier 501 amplifies a single-ended signal.

The multistage amplifier circuit 109 includes the variable gainamplifier 501 (the power amplifier circuit), a power-stage amplifier551, and a gain control circuit 601.

The multistage amplifier circuit 109 is used for amplification of, forexample, an RF signal. In the ninth embodiment, the variable gainamplifier 501 is a drive-stage amplifier. The variable gain amplifier501 amplifies a signal RF5 (an input signal) input into the multistageamplifier circuit 109 through the input terminal 31 and supplies anamplified signal RF6 resulting from amplification of the signal RF5 tothe power-stage amplifier 551.

The power-stage amplifier 551 amplifies the amplified signal RF6amplified by the variable gain amplifier 501 and supplies an amplifiedsignal RF7 resulting from amplification of the amplified signal RF6 toan output terminal 32.

The gain control circuit controls the gain of the amplifier to becontrolled based on the degree of saturation in the amplifier to bedetected. The “control of the gain of the amplifier to be controlledbased on the degree of saturation in the amplifier to be detected” meansthat, when the saturation in the amplifier to be detected is detected,the gain of the amplifier to be controlled is decreased or increased.

The gain control circuit 601 supplies the bias to the power-stageamplifier 551 and controls the gain of the variable gain amplifier 501based on the degree of saturation in the power-stage amplifier 551through analog control. In the ninth embodiment, the gain controlcircuit 601 decreases the gain of the variable gain amplifier 501 upondetection of the saturation in the power-stage amplifier 551.

The multistage amplifier circuit 109 will now be described in detail.FIG. 10 is a circuit diagram of the variable gain amplifier 501. Asillustrated in FIG. 10 , the variable gain amplifier 501 includes acurrent control circuit 14, the first amplifier transistor 201, thecapacitor 202, the resistive element 203, the inductor 204, the diode205 (the first nonlinear circuit element and the first diode), thevoltage power supply 207, and the resistive element 208 (the firstresistive element). The current control circuit 14 includes a transistor308 (a second transistor).

The first amplifier transistor 201, the capacitor 202, the resistiveelement 203, the inductor 204, the diode 205, the voltage power supply207, and the resistive element 208 in the variable gain amplifier 501are the same as the first amplifier transistor 201, the capacitor 202,the resistive element 203, the inductor 204, the diode 205, the voltagepower supply 207, and the resistive element 208 in the power amplifiercircuit 103 illustrated in FIG. 3 .

The transistor 308 in the current control circuit 14 has a collectorconnected to the first end of the capacitor 202, a base connected to thegain control circuit 601, and an emitter that is grounded. The collectorcurrent of the transistor 308 is adjusted using the control signalsupplied from the gain control circuit 601 to the base of the transistor308. Varying the collector current of the transistor 308 enables thecurrent flowing through the diode 205 to be varied.

Since the adjustment of the current flowing through the diode 205 usingthe control signal enables the equivalent resistance value of the diode205 to be adjusted, the amount of feedback of the amplified signal RF6from the collector of the first amplifier transistor 201 to the basethereof is capable of being adjusted. Accordingly, it is possible toadjust the gain of the first amplifier transistor 201.

FIG. 11 is a circuit diagram of the gain control circuit 601. Asillustrated in FIG. 11 , the gain control circuit 601 includes a biassupply circuit 602 and a VGA control circuit 603. The bias supplycircuit 602 includes transistors 611 and 612 and resistive elements 613and 614. The VGA control circuit 603 includes transistors 621, 622, and623 and resistive elements 625 and 626.

A bias supply terminal 616 is connected to, for example, the base of anamplifier transistor (not illustrated) included in the power-stageamplifier 551 (refer to FIG. 9 ). The bias supply circuit 602 suppliesbase potential appropriate for the power-stage amplifier 551 to thepower-stage amplifier 551 via the bias supply terminal 616.Specifically, for example, control current for controlling the bias ofthe power-stage amplifier 551 is externally supplied to a bias controlsignal input terminal 615. Power supply voltage VCC1 is externallysupplied to a power supply voltage supplying node N1.

The transistor 611 has a collector connected to the power supply voltagesupplying node N1, a base connected to the bias control signal inputterminal 615 via the resistive element 613, and an emitter connected tothe bias supply terminal 616.

The transistor 612 has a collector connected to the base of thetransistor 611, a base connected to the emitter of the transistor 611via the resistive element 614, and an emitter that is grounded.

Bias voltage resulting from addition of the base-emitter voltage Vbe ofthe transistor 612 to the voltage between the terminals of the resistiveelement 614 is supplied to the power-stage amplifier 551 via the biassupply terminal 616.

When the power-stage amplifier 551 is saturated, the base currentflowing from the bias supply terminal 616 to the power-stage amplifier551 is increased. At this time, the bias voltage at the bias supplyterminal 616 is decreased. In other words, the bias voltage at the biassupply terminal 616 is used as a detection signal for detecting thesaturation in the power-stage amplifier 551.

The VGA control circuit 603 generates the control signal for controllingthe gain of the variable gain amplifier 501 based on the detectionsignal to supply the generated control signal to the transistor 308.

Specifically, the transistor 621 is diode-connected and has a collectorconnected to a VGA control voltage input terminal 628 via the resistiveelement 625 and an emitter. The transistor 622 is diode-connected andhas a collector connected to the emitter of the transistor 621 and anemitter that is grounded.

The resistive element 626 has a first end connected to the collector ofthe transistor 621 and a second end. The transistor 623 has a collectorconnected to the second end of the resistive element 626 and the base ofthe transistor 308 (refer to FIG. 10 ), a base connected to the emitterof the transistor 611, and an emitter that is grounded.

Voltage for generating reference voltage is externally supplied to theVGA control voltage input terminal 628. Since each of the transistors621 and 622 functions as a diode, voltage drop corresponding to the twodiodes occurs on a path between the collector of the transistor 621 andthe emitter thereof and a path between the collector of the transistor622 and the emitter thereof. In other words, collector voltage of thetransistor 621 based on the ground, that is, the reference voltage isvoltage of a level corresponding to the voltage drop corresponding tothe two diodes.

Collector voltage of the transistor 623 is voltage resulting fromsubtraction of the voltage between the terminals of the resistiveelement 626 from the reference voltage. Current corresponding to thedetection signal supplied to the base of the transistor 623 flowsthrough the resistive element 626.

Specifically, since the saturation in the power-stage amplifier 551decreases the voltage value of the detection signal, the current flowingthrough the resistive element 626 and the collector of the transistor623 is decreased. Accordingly, the voltage between the terminals of theresistive element 626 is decreased to increase the collector voltage ofthe transistor 623, that is, the voltage of the control signal.

As illustrated in FIG. 10 , since the current flowing through the diode205 is increased to reduce the gain of the first amplifier transistor201 when the voltage of the control signal is made high, the power ofthe amplified signal RF6 input into the power-stage amplifier 551 isdecreased. As a result, the power-stage amplifier 551 is released fromthe saturation operation.

For example, when the power-stage amplifier 551 continues the saturationoperation, the communication quality may be reduced or, in the worstcase, the power-stage amplifier 551 may be broken due to distortion ofthe amplified signal RF7. In addition, the power at which thepower-stage amplifier 551 is saturated is varied depending on variousfactors including an output load and the environmental temperature.Accordingly, in design of an amplifier in the related art, which doesnot perform the control against the saturation, it is suitable toincrease the margin for saturation power.

In contrast, in the multistage amplifier circuit 109, the gain controlcircuit 601 performs control so as to reduce the gain of the variablegain amplifier 501 upon detection of the saturation in the power-stageamplifier 551. Since the power-stage amplifier 551 is released from thesaturation operation in this case, it is possible to suppress thereduction in the communication quality and the breaking of thepower-stage amplifier 551. In addition, it is possible to decrease themargin for the saturation power, compared with that in the amplifier inthe related art.

Although the multistage amplifier circuit 109 is described to have theconfiguration including the gain control circuit 601, the configurationof the multistage amplifier circuit 109 is not limited to this. Themultistage amplifier circuit 109 may have a configuration including again control circuit that controls the gain of the variable gainamplifier 501 without detecting the saturation in the power-stageamplifier 551. Such a gain control circuit controls the gain of thevariable gain amplifier 501 based on, for example, the communicationdistance to a base station to increase or decrease transmission power ofthe RF signal.

Although the multistage amplifier circuit 109 is described as thetwo-stage amplifier circuit, the configuration of the multistageamplifier circuit 109 is not limited to this. The multistage amplifiercircuit 109 may be an amplifier circuit of three or more stages. In thiscase, for example, the variable gain amplifier 501 is provided at thefirst stage in the multistage amplifier circuit 109. For example, thegain control circuit 601 supplies the bias to the final-stage amplifierand detects the saturation in the final-stage amplifier.

Although the variable gain amplifier 501 is described to have theconfiguration including the diode 205 and the resistive element 208,which are connected in series to each other, between the collector ofthe first amplifier transistor 201 and the base thereof, theconfiguration of the variable gain amplifier 501 is not limited to this.The variable gain amplifier 501 may have the configuration includingonly the diode 205 (refer to FIG. 1 ) between the collector of the firstamplifier transistor 201 and the base thereof, the configurationincluding the diodes 205 and 209, which are connected in series to eachother (refer to FIG. 4 ) between the collector of the first amplifiertransistor 201 and the base thereof, or the configuration including thevoltage multiplier circuit 210 (refer to FIG. 5 ) between the collectorof the first amplifier transistor 201 and the base thereof.

Tenth Embodiment

A Doherty amplifier circuit 110 according to a tenth embodiment will nowbe described. FIG. 12 is a circuit diagram of the Doherty amplifiercircuit 110. As illustrated in FIG. 12 , the Doherty amplifier circuit110 according to the tenth embodiment differs from the multistageamplifier circuit 109 according to the ninth embodiment in that thevariable gain amplifier 501 is used as a peak-side driver-stageamplifier.

The Doherty amplifier circuit 110 includes the variable gain amplifier501 (the power amplifier circuit), a carrier circuit 561, a peak circuit562, a gain control circuit 604, a splitter 701, and a combiner 711.

The carrier circuit 561 includes a driver-stage carrier amplifier 561 aand a power-stage carrier amplifier 561 b. The peak circuit 562 includesa power-stage peak amplifier 562 a. The carrier circuit 561 may have aconfiguration including three or more carrier amplifiers. The peakcircuit 562 may have a configuration including two or more peakamplifiers.

The splitter 701 splits a signal RF8 (a fifth signal) into a signal RF9(a sixth signal) and a signal RF10 (a seventh signal) having a phasedifferent from that of the signal RF9. In the tenth embodiment, thesplitter 701 is a 90-degree coupler and includes a line 701 a, a line701 b, and a resistive element 701 c.

The line 701 a has a first end into which the signal RF8 is input viathe input terminal 31 and a second end which is connected to the inputterminal of the variable gain amplifier 501 and from which the signalRF10 is output. The line 701 b has a first end which is connected to theinput terminal of the driver-stage carrier amplifier 561 a and fromwhich the signal RF9 is output and a second end that is grounded via theresistive element 701 c. The line 701 b is electromagnetically coupledto the line 701 a. The phase of the signal RF10 is shifted from thephase of the signal RF9 by approximately 90°.

The driver-stage carrier amplifier 561 a in the carrier circuit 561amplifies the signal RF9 supplied from the first end of the line 701 band supplies an amplified signal RF11 resulting from amplification ofthe signal RF9 to the power-stage carrier amplifier 561 b. Thepower-stage carrier amplifier 561 b amplifies the amplified signal RF11and supplies an amplified signal RF13 resulting from amplification ofthe amplified signal RF11 to the combiner 711.

The variable gain amplifier 501 amplifies the signal RF10 supplied fromthe second end of the line 701 a and supplies an amplified signal RF12(an eighth signal) resulting from amplification of the signal RF10 tothe peak circuit 562.

The power-stage peak amplifier 562 a in the peak circuit 562 amplifiesthe amplified signal RF12 supplied from the variable gain amplifier 501and supplies an amplified signal RF14 resulting from the amplificationof the amplified signal RF12 to the combiner 711.

The combiner 711 combines the amplified signal RF13 with the amplifiedsignal RF14 and supplies an output signal RF15, which is the amplifiedsignal of the signal RF8, to the output terminal 32.

In the tenth embodiment, the combiner 711 includes a ¼ wavelength line711 a and a node 711 b. The ¼ wavelength line 711 a has a first endconnected to the output terminal of the power-stage carrier amplifier561 b and a second end connected to the node 711 b. The node 711 b isprovided on a path with which the power-stage peak amplifier 562 a isconnected to the output terminal 32.

FIG. 13 is a circuit diagram of the gain control circuit 604. Asillustrated in FIG. 13 , the gain control circuit 604 further includesan inverting amplifier circuit 605, in addition to the components in thegain control circuit 601 illustrated in FIG. 11 . The invertingamplifier circuit 605 includes a resistive element 627 and a transistor624.

The bias supply terminal 616 is connected to, for example, the base ofan amplifier transistor (not illustrated) included in the power-stagecarrier amplifier 561 b (refer to FIG. 12 ).

The resistive element 627 has a first end connected to the collector ofthe transistor 621 and a second end. The transistor 624 has a collectorconnected to the second end of the resistive element 627 and the base ofthe transistor 308 (refer to FIG. 10 ), a base connected to thecollector of the transistor 623, and an emitter that is grounded.

As illustrated in FIG. 12 and FIG. 13 , the gain control circuit 604supplies the bias to the power-stage carrier amplifier 561 b closest tothe output side in the carrier circuit 561 and controls the gain of thevariable gain amplifier 501 based on the degree of saturation in thepower-stage carrier amplifier 561 b through the analog control.

In the tenth embodiment, the gain control circuit 604 performs controlso as to increase the gain of the variable gain amplifier 501 upondetection of the saturation in the power-stage carrier amplifier 561 b.Specifically, the inverting amplifier circuit 605 supplies the controlsignal resulting from inverting amplification of the collector voltageof the transistor 623 to the transistor 308 (refer to FIG. 10 ). Asdescribed above, when the power-stage amplifier 551 is saturated, thecollector voltage of the transistor 623 is increased. In other words,the voltage of the control signal supplied from the inverting amplifiercircuit 605 to the transistor 308 is decreased when the power-stageamplifier 551 is saturated.

As illustrated in FIG. 10 and FIG. 12 , since the current flowingthrough the diode 205 is decreased and the gain of the first amplifiertransistor 201 is increased upon decrease of the voltage of the controlsignal, the power of the amplified signal RF12 input into thepower-stage peak amplifier 562 a is increased. Accordingly, the Dohertyamplifier circuit 110 operates so that the power output from thepower-stage peak amplifier 562 a is increased when the power-stagecarrier amplifier 561 b is saturated.

The power-stage carrier amplifier 561 b is released from the saturationstate due to the effect of load modulation of the Doherty amplifiercircuit 110. Since this enables the continuous saturation in thepower-stage carrier amplifier 561 b to be suppressed, it is possible tosuppress the reduction in the communication quality and the breaking ofthe power-stage carrier amplifier 561 b.

With the configuration in which an increase in the base current of thepower-stage carrier amplifier 561 b, which causes the saturation in thepower-stage carrier amplifier 561 b, is detected, it is possible toshorten the time from the saturation in the power-stage carrieramplifier 561 b to completion of the control to increase the gain of thevariable gain amplifier 501.

Exemplary embodiments of the present disclosure are described above. Inthe multistage amplifier circuit 109 or the Doherty amplifier circuit110, the first amplifier transistor 201 has the base into which thesignal RF5 is input, the collector from which the amplified signal RF6resulting from amplification of the signal RF5 is output, and theemitter that is grounded. The first nonlinear circuit element isconnected between the collector of the first amplifier transistor 201and the base of the first amplifier transistor 201. The current controlcircuit 14 is connected between the ground and the base of the firstamplifier transistor 201 to control the current flowing through thefirst nonlinear circuit element.

As described above, the equivalent resistance value of the firstnonlinear circuit element is capable of being varied with the simplecircuit configuration in which the current flowing through the firstnonlinear circuit element is controlled by the current control circuit14. This enables the amount of feedback of the amplified signal RF6 fromthe collector of the first amplifier transistor 201 to the base thereofto be adjusted. Since the power of the signal RF5 is capable of beingdecreased with the amplified signal RF6 having voltage polarity oppositeto that of the signal RF5, the increase in the amount of feedbackenables the gain of the first amplifier transistor 201 to be decreased.Accordingly, it is possible to realize the adjustment of the gain in theamplification of the input signal with the simple circuit configuration.

In the multistage amplifier circuit 109 or the Doherty amplifier circuit110, the first nonlinear circuit element is the diode 205 having theanode connected to the collector of the first amplifier transistor 201and the cathode connected the base of the first amplifier transistor201.

With the above configuration, it is possible to simply realize the firstnonlinear circuit element capable of varying the equivalent resistancevalue with the flowing current.

The multistage amplifier circuit 109 or the Doherty amplifier circuit110 further includes the resistive element 208, which is connected inseries or in parallel to the diode 205, between the collector of thefirst amplifier transistor 201 and the base of the first amplifiertransistor 201.

As described above, with the configuration in which the diode 205 isconnected in series to the resistive element 208, the lower limit of thecombined resistance value of the resistive element 208 and the diode 205is capable of being adjusted with the resistance value of the resistiveelement 208. Accordingly, it is possible to adjust the lower limit ofthe gain of the first amplifier transistor 201. In addition, with theconfiguration in which the diode 205 is connected in parallel to theresistive element 208, the upper limit of the combined resistance valueof the resistive element 208 and the diode 205 is capable of beingadjusted with the resistance value of the resistive element 208.Accordingly, it is possible to adjust the upper limit of the gain of thefirst amplifier transistor 201.

The multistage amplifier circuit 109 or the Doherty amplifier circuit110 further includes the diode 209, which is connected in series to thediode 205 between the collector of the first amplifier transistor 201and the base of the first amplifier transistor 201.

With the above configuration, the variable range of the combinedresistance value of the diodes 205 and 209 is capable of being increasedto approximately two times of the variable range of the equivalentresistance value of the diode 205. Accordingly, it is possible to widenthe adjustment range of the gain of the first amplifier transistor 201and to increase the maximum gain.

In addition, in the multistage amplifier circuit 109 or the Dohertyamplifier circuit 110, the first nonlinear circuit element includes thetransistor 210 a having the collector connected to the collector of thefirst amplifier transistor 201, the base, and the emitter connected tothe base of the first amplifier transistor 201. The resistive element210 b is connected between the collector of the transistor 210 a and thebase of the transistor 210 a. The resistive element 210 c is connectedbetween the base of the transistor 210 a and the emitter of thetransistor 210 a.

With the above configuration, appropriately selecting the resistancevalue of the resistive element 210 b and the resistance value of theresistive element 210 c enables the voltage between the collector andthe emitter of the transistor 210 a to be substantially fixed to thevoltage corresponding to these resistance values. Adjusting the currentflowing through the resistive elements 210 b and 210 c and thetransistor 210 a enables the equivalent resistance value between thecollector and the emitter of the transistor 210 a to be adjusted. Inother words, it is possible to adjust the gain of the first amplifiertransistor 201. In addition, since the voltage between the collector andthe emitter of the transistor 210 a is capable of being arbitrarily set,the range of the equivalent resistance value between the collector andthe emitter of the transistor 210 a is capable being adjusted. In otherwords, it is possible to adjust the range of the gain of the firstamplifier transistor 201. Consequently, it is possible to improve thedegree of freedom of design of the multistage amplifier circuit 109 orthe Doherty amplifier circuit 110.

In the multistage amplifier circuit 109 or the Doherty amplifier circuit110, the current control circuit 14 includes the transistor 308 havingthe collector connected to the base of the first amplifier transistor201, the base into which the control signal is input, and the emitterthat is grounded.

With the above configuration, it is possible to simply realize theconfiguration in which increase and decrease of the current flowingthrough the first nonlinear circuit element is controlled with thecontrol signal.

In the power amplifier circuits 101 to 107, the second amplifiertransistor 251 has the base into which the signal RFm1 having the phasedifferent from that of the signal RFp1 is input, the collector fromwhich the amplified signal RFm2 resulting from amplification of thesignal RFm1 is output, and the emitter that is grounded. The secondnonlinear circuit element is connected between the collector of thesecond amplifier transistor 251 and the base of the second amplifiertransistor 251. The current control circuit 11, 12, or 13 is connectedbetween the ground, and the base of the first amplifier transistor 201and the base of the second amplifier transistor 251 and controls thecurrent flowing through the first nonlinear circuit element and thecurrent flowing through the second nonlinear circuit element.

With the above configuration, it is possible to realize the variablegain differential amplifier circuit with the simple circuitconfiguration.

In the power amplifier circuit 108, the first amplifier transistor 201has the base into which the signal RFp1 is input, the collector fromwhich the amplified signal RFp2 resulting from amplification of thesignal RFp1 is output, and the emitter that is grounded. The secondamplifier transistor 251 has the base into which the signal RFm1 havinga phase different from that of the signal RFp1 is input, the collectorfrom which the amplified signal RFm2 resulting from amplification of thesignal RFm1 is output, and the emitter that is grounded. The firstnonlinear circuit element is connected between the collector of thesecond amplifier transistor 251 and the base of the first amplifiertransistor 201. The second nonlinear circuit element is connectedbetween the collector of the first amplifier transistor 201 and the baseof the second amplifier transistor 251. The current control circuit 11,12, or 13 is connected between the ground, and the base of the firstamplifier transistor 201 and the base of the second amplifier transistor251 and controls the current flowing through the first nonlinear circuitelement and the current flowing through the second nonlinear circuitelement.

As described above, with the configuration in which the first nonlinearelement having the junction capacitance is connected between thecollector of the second amplifier transistor 251 and the base of thefirst amplifier transistor 201, the amplified signal RFm2 is capable ofbeing supplied from the collector of the second amplifier transistor 251to the base of the first amplifier transistor 201 via the junctioncapacitance. Accordingly, the amplified signal RFp2 returning from thecollector of the first amplifier transistor 201 to the base thereof viathe junction capacitance 201 a is capable of being canceled with theamplified signal RFm2 having a phase opposite to that of the amplifiedsignal RFp2. Consequently, it is possible to suppress the reduction inthe gain of the first amplifier transistor 201 and the degradation ofthe input dependency of the pass phase characteristics. In addition,with the configuration in which the second nonlinear circuit elementhaving the junction capacitance is connected between the collector ofthe first amplifier transistor 201 and the base of the second amplifiertransistor 251, the amplified signal RFp2 is capable of being suppliedfrom the collector of the first amplifier transistor 201 to the base ofthe second amplifier transistor 251 via the junction capacitance.Accordingly, the amplified signal RFm2 returning from the collector ofthe second amplifier transistor 251 to the base thereof via the junctioncapacitance 251 a is capable of being canceled with the amplified signalRFp2 having a phase opposite to that of the amplified signal RFm2.Consequently, it is possible to suppress the reduction in the gain ofthe second amplifier transistor 251 and the degradation of the inputdependency of the pass phase characteristics.

In the current control circuit 12 in the power amplifier circuits 102 to106 and the power amplifier circuit 108, the primary-side inductor 402has the first end and the second end. The inductor 403 a iselectromagnetically coupled to the primary-side inductor 402 and has thefirst end connected to the base of the first amplifier transistor 201and the second end. The inductor 403 b is electromagnetically coupled tothe primary-side inductor 402 and has the first end connected to thesecond end of the inductor 403 a and the second end connected to thebase of the second amplifier transistor 251. The transistor 304 has thecollector connected to the second end of the inductor 403 a and thefirst end of the inductor 403 b, the base into which the control signalis input, and the emitter that is grounded.

With the above configuration, since output of the radio-frequency signalfrom the node between the inductor 403 a and the inductor 403 b to thetransistor 304 is suppressed, reflection of the radio-frequency signalby the parasitic capacitance 304 a of the transistor 304 is suppressed.Accordingly, the reduction in the quality of the radio-frequency signaland an occurrence of malfunction are capable of being suppressed. Inaddition, the potential of the base, which is higher than the potentialof the collector, is capable of being suppressed in the transistor 304.Accordingly, it is possible to suppress shift of the bias points of thefirst amplifier transistor 201 and the second amplifier transistor 251and unstable current flowing through the first nonlinear circuit elementand the second nonlinear circuit element. In other words, it is possibleto realize the variable gain differential amplifier circuit thatoperates well for the radio-frequency signal.

In the current control circuit 12 in the power amplifier circuits 102 to106 and the power amplifier circuit 108, the inductor 403 a hasapproximately the same inductance as the inductance of the inductor 403b.

With the above configuration, since output of the radio-frequency signalfrom the node between the inductor 403 a and the inductor 403 b to thetransistor 304 is made approximately zero, the reduction in the qualityof the radio-frequency signal and an occurrence of malfunction arecapable of being prevented. In addition, it is possible to prevent theshift of the bias points of the first amplifier transistor 201 and thesecond amplifier transistor 251 and to stabilize the current flowingthrough the first nonlinear circuit element and the second nonlinearcircuit element.

In the current control circuit 12 in the power amplifier circuits 102 to105 and the power amplifier circuit 108, the signal RFp3 is input intothe first end of the primary-side inductor 402. The signal RFm3 having aphase different from that of the signal RFp3 is input into the secondend of the primary-side inductor 402.

With the above configuration, since the primary-side inductor 402 andthe inductors 403 a and 403 b function as matching circuits, it ispossible to realize the variable gain differential amplifier circuitthat operates well for the differential signal in a high-frequency band.

In the current control circuit 12 in the power amplifier circuit 106,the signal RF4 is input into the first end of the primary-side inductor402. The second end of the primary-side inductor 402 is grounded.

With the above configuration, since the primary-side inductor 402 andthe inductors 403 a and 403 b function as a balun, it is possible torealize the variable gain differential amplifier circuit that operateswell for the single-ended signal in a high-frequency band.

The current control circuit 11 in the power amplifier circuit 101include the transistors 302 and 303. The transistor 302 has thecollector connected to the base of the first amplifier transistor 201,the base into which the control signal is input, and the emitter that isgrounded. The transistor 303 has the collector connected to the base ofthe second amplifier transistor 251, the base connected to the base ofthe transistor 302, and the emitter that is grounded.

With the above configuration, the current flowing through each of thefirst nonlinear circuit element and the second nonlinear circuit elementis capable of being adjusted with the collector current of thetransistor 302 and the collector current of the transistor 303. Thecollector current is capable of being adjusted through simple control inwhich the control signal is supplied to the bases of the transistors 302and 303. In other words, it is possible to adjust the current flowingthrough each of the first nonlinear circuit element and the secondnonlinear circuit element through the simple configuration and control.

The current control circuit 13 in the power amplifier circuit 107includes the inductors 305 and 306 and the transistor 307. The inductor305 has the first end connected to the base of the first amplifiertransistor 201 and the second end. The inductor 306 has the first endconnected to the base of the second amplifier transistor 251 and thesecond end. The transistor 307 has the collector connected to the secondend of the inductor 305 and the second end of the inductor 306, the baseinto which the control signal is input, and the emitter that isgrounded.

With the above configuration, the current flowing through each of thefirst nonlinear circuit element and the second nonlinear circuit elementis capable of being adjusted with the collector current of thetransistor 307 while suppressing short-circuiting of the base of thefirst amplifier transistor 201 and the base of the second amplifiertransistor 251 with an alternating current signal. The collector currentis capable of being adjusted through the simple control in which thecontrol signal is supplied to the base of the transistor 307. In otherwords, it is possible to adjust the current flowing through each of thefirst nonlinear circuit element and the second nonlinear circuit elementthrough the simpler configuration and control.

In the Doherty amplifier circuit 110, the splitter 701 splits the signalRF8 into the signal RF9 and the signal RF10 having a phase differentfrom that of the signal RF9. The carrier circuit 561 includes two ormore carrier amplifiers. The carrier circuit 561 amplifies the signalRF9 and outputs the amplified signal RF13 resulting from amplificationof the signal RF9. The variable gain amplifier 501 amplifies the signalRF10 and outputs the amplified signal RF12 resulting from amplificationof the signal RF10. The peak circuit 562 includes one or more peakamplifiers. The peak circuit 562 amplifies the amplified signal RF12supplied from the variable gain amplifier 501 and outputs the amplifiedsignal RF14 resulting from amplification of the amplified signal RF12.The gain control circuit 604 controls the gain of the variable gainamplifier 501 based on the degree of saturation in the power-stagecarrier amplifier 561 b closest to the output side in the carriercircuit 561.

With the above configuration, for example, when the saturation in thepower-stage carrier amplifier 561 b is detected by the gain controlcircuit 604, the gain of the variable gain amplifier 501 is capable ofbeing increased. This avoids continuation of a situation in which thepeak circuit 562 does not operate despite the saturation in thepower-stage carrier amplifier 561 b. Since the power-stage carrieramplifier 561 b is released from the saturation state due to the effectof the load modulation of the Doherty amplifier circuit 110, it ispossible to suppress the reduction in the communication quality and thebreaking, which are caused by the continuous saturation in thepower-stage carrier amplifier 561 b.

In the multistage amplifier circuit 109, the variable gain amplifier 501amplifies the signal RF5 and outputs the amplified signal RF6 resultingfrom amplification of the signal RF5. The power-stage amplifier 551amplifies the signal RF5 amplified by the variable gain amplifier 501,that is, the amplified signal RF6. The gain control circuit 601 controlsthe gain of the variable gain amplifier 501.

With the above configuration, since the gain of the variable gainamplifier 501 is capable of being adjusted through external control, itis possible to increase or decrease the transmission power of the RFsignal based on, for example, the communication distance to the basestation.

In the multistage amplifier circuit 109, the gain control circuit 601controls the gain of the variable gain amplifier 501 based on the degreeof saturation in the power-stage amplifier 551.

With the above configuration, for example, when the saturation in thepower-stage amplifier 551 is detected by the gain control circuit 601,the gain of the variable gain amplifier 501 is capable of beingdecreased. Since this releases the power-stage amplifier 551 from thesaturation state, it is possible to suppress the reduction in thecommunication quality and the breaking, which are caused by thecontinuous saturation in the power-stage amplifier 551.

The power amplifier apparatus includes the compound semiconductor 1having semiconductor devices formed therein and thereon. Thesemiconductor devices are included in one of the power amplifiercircuits 101 to 108, the multistage amplifier circuit 109, or theDoherty amplifier circuit 110.

With the above configuration, the control of the current flowing throughthe first nonlinear circuit element or the second nonlinear circuitelement and the detection of the saturation in the amplifier are capableof being performed with an analog signal without using a digital signal.Since this enables the control without any processing, such asconversion of data and calculation, for example, it is possible tocomplete the processing from the detection of the saturation in theamplifier to the control of the gain for a very short time. Accordingly,since the time when the saturation in the amplifier occurs is shortened,it is possible to suppress degradation in the quality of the amplifiedsignal. In addition, since the formation of each semiconductor device onthe same compound semiconductor 1 shortens the transmission distance ofthe signals exchanged between the semiconductor devices, it is possibleto realize higher-speed control.

The respective embodiments are described above for facilitating theunderstanding of the present disclosure and are not intended to limitthe interpretation of the present disclosure. Modifications and/orchanges of the present disclosure may be made without departing from theintent of the present disclosure and equivalents are also included inthe present disclosure. In other words, embodiments appropriatelysubjected to design change by the person skilled in the art are alsoincluded in the scope of the present disclosure as long as they havefeatures of the present disclosure. For example, the components in therespective embodiments and the arrangement, the materials, theconditions, the shapes, the sizes, and so on of the components are notlimited to the ones that are exemplified and may be appropriatelymodified. The respective embodiments are only examples, and partialreplacement or combination of the components described in differentembodiments is available and is included in the scope of the presentdisclosure as long as it has features of the present disclosure.

What is claimed is:
 1. A power amplifier circuit comprising: a firstamplifier transistor having a base or a gate into which a first signalis input, a collector or a drain from which a first amplified signalresulting from amplification of the first signal is output, and anemitter or a source that is grounded; a first nonlinear circuit elementconnected between the collector or the drain of the first amplifiertransistor and the base or the gate of the first amplifier transistor;and a current control circuit connected between ground and the base orthe gate of the first amplifier transistor, and configured to controlcurrent flowing through the first nonlinear circuit element.
 2. Thepower amplifier circuit according to claim 1, wherein the firstnonlinear circuit element is a first diode having an anode connected tothe collector or the drain of the first amplifier transistor and acathode connected to the base or the gate of the first amplifiertransistor.
 3. The power amplifier circuit according to claim 2, furthercomprising: a first resistive circuit element connected in series or inparallel with the first diode between the collector or the drain of thefirst amplifier transistor and the base or the gate of the firstamplifier transistor.
 4. The power amplifier circuit according to claim2, further comprising: a second diode connected in series with the firstdiode between the collector or the drain of the first amplifiertransistor and the base or the gate of the first amplifier transistor,and having an anode connected to the collector or the drain of the firstamplifier transistor and a cathode connected to the base or the gate ofthe first amplifier transistor.
 5. The power amplifier circuit accordingto claim 1, wherein the first nonlinear circuit element comprises afirst transistor having a collector or a drain connected to thecollector or the drain of the first amplifier transistor, a base or agate, and an emitter or a source connected to the base or the gate ofthe first amplifier transistor, and wherein the power amplifier circuitfurther comprises: a second resistive circuit element connected betweenthe collector or the drain of the first transistor and the base or thegate of the first transistor; and a third resistive circuit elementconnected between the base or the gate of the first transistor and theemitter or the source of the first transistor.
 6. The power amplifiercircuit according to claim 1, wherein the current control circuitcomprises: a second transistor that has a collector or a drain connectedto the base or the gate of the first amplifier transistor, a base or agate into which a control signal is input, and an emitter or a sourcethat is grounded.
 7. A power amplifier circuit comprising: a firstamplifier transistor having a base or a gate into which a first signalis input, a collector or a drain from which a first amplified signalresulting from amplification of the first signal is output, and anemitter or a source that is grounded; a second amplifier transistorhaving a base or a gate into which a second signal is input, a collectoror a drain from which a second amplified signal resulting fromamplification of the second signal is output, and an emitter or a sourcethat is grounded; a first nonlinear circuit element connected betweenthe collector or the drain of the second amplifier transistor and thebase or the gate of the first amplifier transistor; a second nonlinearcircuit element connected between the collector or the drain of thefirst amplifier transistor and the base or the gate of the secondamplifier transistor; and a current control circuit connected betweenground and the base or the gate of the first amplifier transistor, andbetween ground and the base or the gate of the second amplifiertransistor, the current control circuit being configured to controlcurrent flowing through the first nonlinear circuit element and currentflowing through the second nonlinear circuit element, wherein the secondsignal has a different phase than the first signal.
 8. The poweramplifier circuit according to claim 7, wherein the current controlcircuit comprises: a first line that has a first end and a second end; asecond line that is electromagnetically coupled to the first line andthat has a first end connected to the base or the gate of the firstamplifier transistor and a second end; a third line that iselectromagnetically coupled to the first line and that has a first endconnected to the second end of the second line and a second endconnected to the base or the gate of the second amplifier transistor;and a third transistor that has a collector or a drain connected to thesecond end of the second line and the first end of the third line, abase or a gate into which a control signal is input, and an emitter or asource that is grounded.
 9. The power amplifier circuit according toclaim 8, wherein the second line has approximately the same inductanceas an inductance of the third line.
 10. The power amplifier circuitaccording to claim 8, wherein a third signal is input into the first endof the first line, and wherein a fourth signal is input into the secondend of the first line, the fourth signal having a different phase thanthe third signal.
 11. The power amplifier circuit according to claim 8,wherein a third signal is input into the first end of the first line,and wherein the second end of the first line is grounded.
 12. The poweramplifier circuit according to claim 7, wherein the current controlcircuit comprises: a fourth transistor that has a collector or a drainconnected to the base or the gate of the first amplifier transistor, abase or a gate into which a control signal is input, and an emitter or asource that is grounded, and a fifth transistor that has a collector ora drain connected to the base or the gate of the second amplifiertransistor, a base or a gate connected to the base or the gate of thefourth transistor, and an emitter or a source that is grounded.
 13. Thepower amplifier circuit according to claim 7, wherein the currentcontrol circuit comprises: a first impedance circuit element that has afirst end connected to the base or the gate of the first amplifiertransistor and a second end; a second impedance circuit element that hasa first end connected to the base or the gate of the second amplifiertransistor and a second end connected to the second end of the firstimpedance circuit element; and a sixth transistor that has a collectoror a drain connected to the second end of the first impedance circuitelement and the second end of the second impedance circuit element, abase or a gate into which a control signal is input, and an emitter or asource that is grounded.
 14. A Doherty amplifier circuit comprising: asplitter configured to split a fifth signal into a sixth signal and aseventh signal, the seventh signal having a different phase than thesixth signal; a carrier circuit comprising two or more carrieramplifiers, and configured to amplify the sixth signal, and to output afirst amplified signal resulting from amplification of the sixth signal;the power amplifier circuit according to claim 1, the power amplifiercircuit being configured to amplify the seventh signal and to output aneighth signal resulting from amplification of the seventh signal; a peakcircuit comprising one or more peak amplifiers, and configured toamplify the eighth signal output from the power amplifier circuit, andto output a second amplified signal resulting from amplification of theeighth signal; and a gain control circuit configured to control a gainof the power amplifier circuit based on a degree of saturation in thecarrier amplifier closest to an output side in the carrier circuit. 15.A multistage amplifier circuit comprising: the power amplifier circuitaccording to claim 1, the power amplifier circuit being configured toamplify an input signal and to output a signal resulting fromamplification of the input signal; an amplifier configured to amplifythe input signal amplified by the power amplifier circuit; and a gaincontrol circuit configured to control a gain of the power amplifiercircuit.
 16. The multistage amplifier circuit according to claim 15,wherein the gain control circuit is configured to control the gain ofthe power amplifier circuit based on a degree of saturation in theamplifier.